Grid for electron tubes



Jan. 11, 1955 E. COHN 2,699,518

GRID FOR ELECTRON TUBES Filed March 19, 1952 GRID PLATINUM RUTHENIUMALLOY IIIIIIIIIIIIIIIIII,

INVENTOR Eugene 0072 BY WWW United States Patent GRID FOR ELECTRON TUBESEugene Cohn, White Plains, N. Y. Application March 19, 1952, Serial No.277,402 3 Claims. (Cl. 313-300) This invention relates to electrontubes, and more particularly to miniature and subminiature electrontubes having one or more grids therein. By a miniature electron tube ismeant an electron tube, the envelope of which has a height not exceedingapproximately 1 /2 inches and an outside diameter not exceeding about/51 inch, and by a subminiature electron tube is means an electron tubethe envelope of not exceeding about 1 /2 inches and not exceeding aboutinch.

In the manufacture of miniature and subminiature electron tubessuccessive convolutions of the grids employed therein are usually spacedapart minute distances. Also the distance between the grids or betweenthe innermost grid and the cathode is very small. Such c ose spacing, inoperation of the tube, to meet commercial specifications must bemaintained within a tolerance of the order of only .0005 inch. The gridwire must have adequate tensile strength to permit winding under thenecessary tension to maintain such spacing within the tolerances abovenoted during cleaning, sizing and other handling to which the grids aresubiected in the manufacture of the tube. Also the grid wire must havethe necessary physical character istics to remain in the desired spacedrelationship relative to successive convolutions of the grid and to theother parts of the tube during operation of the tube at the elevatedtemperatures which then occur due, for example, to heating of thecathode. The grid wire must also have the property of not developingharmful oxides when the grid is made and also during subsequent heattreatment employed in making the tube; for example, to etfect itsexhausting. In use, the grid shou d not emit electrons in sutficientquantities to deleteriously affect the operation of the electron tube;this phenomenon is commonly known as and will be hereinafter referred toas secondary emission.

In the manufacture of electron tubes, and particularly the miniature andsubminiature electron tubes, it is now conventional practice to producethe grid from tungsten Wire coated with a precious metal, such as gold,palladium, rhodium or platinum, usually gold. The precious metal coatingis employed to minimize the formation of harmful oxides and to reducesecondary emission; the tungsten base is employed to obtain thenecessary tensile strength. Such grids have been found objectionable fora number of reasons among which may be mentioned it is frequentlynecessary to operate the cathode at such high temperatures thatvaporization of the plated gold takes place with consequent impairmentof the operation of the tube. Furthermore, the tungsten grid wire ofnecessity must be made by a powder metallurgy technique. This results ina wire that is not uniform throughout its length, i. e., the wire hasbrittle or weak spots along its length. Such variations in the wirecause difiiculties when the wire is wound to form a grid; for example,brittle spots in the wire may deleteriously affect the aforesaid spacingor result in the wire breaking as it is wound to form the grid.

It is an object of this invention to provide an electron tube having oneor more grids therein, which in use show no harmful secondary emission,conform with existing tolerances, can be operated without harmfuleffects at materially higher temperatures than heretofore known gridsincluding the commonly used gold plated which has a height an outsidediameter tungsten grid, and do not develop harmful oxides duringfabrication of the electron tube or in use thereof.

Other objects and advantages of this invention will be apparent from thefollowing detailed description thereof.

In accordance with this invention the grid or grids of the electrontubes are made by winding a wire consisting of an alloy containing from5% to 10% ruthenium and from to platnium, the wire having a diameter offrom .0015.0004 inch under tension about the grid supports to producethe grid winding. The alloy is produced by melting the platinum andruthenium constituents in the proportions within the range above noted,producing an ingot from the melt, then wire drawing and annealingbetween successive Wire drawing operations to produce a grid wire of thedesired diameter within the range above noted. As the production of thewire may be in accordance with any well known procedure for producingfine wire of maximum tensile strength, it is believed furtherdescription thereof would serve no useful purpose.

The platinum constituent of the alloy may be pure platinum or anycommercial grade of platinum, preferably Grade 4 Platinum, containing aminimum of 99% platinum, the rest being impurities, such as ruthenium,palladium or other impurities found in platinum. The ruthenium used maybe pure ruthenium or a commercial grade of ruthenium containing smallamounts of impurities. Preferred alloys contain 90% to 92.5% platinumand 7%% to 10% ruthenium, although, as above noted, the proportions maybe varied within the range of from 90% to 95% platinum and 5% to 10%ruthenium. Melting of the platinum and ruthenium to produce an alloyingot which is wire drawn to a diameter size of from .0015 to .0004 inchand annealing between successive wire drawing operations results in awire having a surprisingly high tensile strength, e. g., over 300,000pounds per square inch and usually about 360,000 pounds per square inchin the case of a wire having a diameter of .001 inch.

The accompanying drawing shows, for purposes of illustration only, anelectron tube of the pentode type. In this drawing Figure 1 is aperspective view on an enlarged scale showing a conventional type ofelectron tube in which the invention may be embodied, the glass envelopebeing broken away to show the interior structure of the tube;

Figure 2 is a fragmentary perspective view on a still larger scaleshowing the relative arrangement of the grids, cathode and plate; and

Figure 3 is a horizontal section taken ing through line 3-3 of Figure 2.

Referring to the drawing, 10 indicates a glass bulb or envelope whichencloses the five electrodes of the tube. The electrode assembly ismounted in the usual way on the base 11 which carries a heated cathode12, a control grid 13, a screen grid 14, a suppresser grid 15 and aplate 16 all surrounding the cathode 12. Suitable spacers 17 and 18space the electrodes from each other and prevent lateral displacement ofthe assembly in the tube.

Spaced rods 19 and 20 are suitably supported at their ends in thespacers 17 and 18 and provide supports for the successive convolutionsof the grid wire wound thereabout to form the control grid 13. This wireis wound under tension sufiicient to maintain successive convolutions ofthe wire in desired spaced relation and also to maintain the desiredspacing between the control grid 13 and the cathode 12 and between thecontrol and screen grids. Similarly, spaced rods 21 and 22 providesupports for the convolutions of the grid wire forming the screen gridand supports 23 and 24 provide supports for the convolutions of the gridwire forming the suppresser grid. Some or all of these supporting rodsmay be provided with spaced niches or serrations for receiving andholding the wire wound thereabout, as is well known in this art.

Leads 25 extend from the plate, grids and cathode as is conventional.Since the construction of the electron tube apart from the compositionof the grid wire may be of any well known type, it is believed furtherdescription thereof is unnecessary.

in a plane passscreen grids and, if' desired; alsothe In accordance withthe invention the control and are made by winding the ruthenium platinumalloy hereinabove described about the grid supports under tensionsuflicient to maintain; the: grid.- wire in place." on the: gridsupports;v The tension used Willi depend. on the structureofithe-grichsupports, thezdesignzof the. tube,

suppresser "gridetc.. In:v-iew'of.the hightcnsile strengthzofthezplatinurnruthenium alloys, the grid wire can readily be: woundabout: itssupports. under; tension as high; as: 300,000 pounds. persquare inch; without. danger of: the' wire breaking and thewound'wire'will remain in the desired spaced relationship on. the:grid'. supports.

In. use: it: has been found that grids. made of the ruthenium-platinumalloys do: notxdevelopt harmfult sec ondary emission oroxides- Further,the gridwire; has the: necessary tensile strength and other physical:propertiesto maintain-the aforesaid spacing'within the tolerance above'noted. during the handling of the grids necessary in orderrto mount thegrids withinthevacuum tubes and also; inuse of the tubes evenat therelatively high. temperatures at which the cathode may beeperated;Since: the grid wire is. produced from an alloy melt: and not by ametallurgical technique, it" is 11111 form initsphysical properties. andchemical composition throughout its length; Because. of: this greateruniformity it can be wound with less danger of. breaking and willmaintain the aforesaid spacing within the toleranceabove. noted muchmoreeffectively than the gold.

plated tungsten wire heretofore used.

WhileI have: described myimprovement iIll connection with the grid of aminiature or subminiature electron tube, it' will be understood theinvention is applicable tothe production. of. grids. of other electron.

tubes.

Ordinary commercial platinum and ruthenium often contain: traces ofother. metals, such as gold or: silver. Hence, the presence of tracequantities; of such. other 4.. metals in the alloy is not to beconstrued as a departure from the -scopeand' spiritoftheinvention;

Since different embodiments of the invention could be made withoutdeparting from the scope of this invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. A grid electrode suitable for use in an electron tube consisting ofan alloy wire having a diameter from .0015 to. .0004 inch, the. alloyconsisting of from 5% to 10% ruthenium and from to platinum.

2. A grid electrode: suitable for: use in an electron tube consistingofan alloy wire having a diameter from .0015 to .0004 inch, the alloyconsisting of from 7.5% to 10% ruthenium and from 90% to 92.5% platinum.

3. Anelectron tube having a. cathode; a'COHtIOI. grid, a screen grid, asuppresser grid. andia-plate surrounding the cathode, the control gridand screen grid. being composed. of an. alloy wire. having a diameterfrom .0015to..0.004 inch,,the a11oy consisting of from7.5% to 10%.ruthenium and from.90%. to 92.5% platinum OTHER REFERENCES MetalIndustry, Platinum Metals, April 2, 1948, pages 267, 268.. Copy in.Scientific Library.

